Technical Field
This application is related to a tandem solar cell structure.
Description of the Related Art
The solar cell is an energy transferring optoelectronic device that receives sunlight and transfers it into electrical energy.
The tandem solar cell or the multi junction solar cell stacks two or more than two p-n junction elements in series with the same or different energy bandgaps. In general, the p-n junction element which can absorb higher energy spectrum is formed as the upper layer; the p-n junction element which can absorb lower energy spectrum is formed as the bottom layer. By combining the p-n junction elements of different materials, the photon energy can be absorbed layer by layer. It can raise the absorbing rate and efficiency, and decrease the transferring loss.
FIG. 1 illustrates a cross-sectional view of the conventional tandem solar cell structure including a substrate 101, a buffer layer 102, a tunnel junction 103 and a p-n junction 104. Currently, the wildly used tunnel junction 103 includes a heavily doped n-type layer (n++) 1031 and a heavily doped p-type layer (p++) 1032 wherein the heavily doped n-type layer (n++) is generally doped with Silicon, Tellurium or Selenium. The heavily doped p-type layer (p++) 1032 is generally doped with Carbon, Zinc, Magnesium or Beryllium. The lattice constant of the heavily doped p-type layer (p++) 1032 is decreased after doped with Carbon. It increases the lattice constant difference of the tunnel junction 103 and the substrate 101 and impairs the epitaxial quality and the effect of the tunnel junction 103.